Any ideas to make a DIY string stiffness tester?

[ryohazuki222]

Addressed to the nerds that use the TWU string database. In particular, the stiffness measurement.

Anyone have ideas on how to make a DIY contraption at home to measure string stiffness?

Note: I’m not talking about DT from an ERT or any sort of tension measurement. I’m talking about the string stiffness (not stringbed stiffness) of a given string at a given tension on a given impact — ie, what TWU is doing for their database.

 

[Stringway Official]

Measuring the stiffness of strings can be done easily with a mechanical tension unit. This picture shows the set up that we use to measure the elongation characteristic resulting in the sort of test results below:

The test can also be done without the measuring tool by marking the string, I will be happy to explain that.

The good thing about doing the test is that you can determine the major quality figure being the relation between elastic and remaining elongation.
( 3rd column from the right)

 

[Irvin]

This may help http://www.physics.usyd.edu.au/~cross/PUBLICATIONS/14. StringTests.PDF

 

[ryohazuki222]

Measuring the stiffness of strings can be done easily with a mechanical tension unit. This picture shows the set up that we use to measure the elongation characteristic resulting in the sort of test results below:

The test can also be done without the measuring tool by marking the string, I will be happy to explain that.

The good thing about doing the test is that you can determine the major quality figure being the relation between elastic and remaining elongation.
( 3rd column from the right)

Do you ever measure the stiffness from deflection? I could see making a setup like this using my stringer set at a certain tension.

But I don’t have ideas on how to strike the string with a brief impact and measure the deflection.

Or could you just measure the string elongation after said impact and then calculate the deflection amount??

(Could you translate the columns and explain the valuation the table? Is there a pdf version you have you can share?)

 

[ryohazuki222]

This may help http://www.physics.usyd.edu.au/~cross/PUBLICATIONS/14. StringTests.PDF

It helps a ton. But I’m still stuck on ideas a bit. In particular, I’m not understand the “hammer” they built.

 

[Irvin]

It helps a ton. But I’m still stuck on ideas a bit. In particular, I’m not understand the “hammer” they built.

Sounds like you’re more interested in string elongation only. If you’re going to stretch a string under tension it will be hard to duplicate a sudden impact with the hammer / pendulum of some kind. You could use a DW and with the string under tension add or drop another weight.

 

[Stringway Official]

IMO: In mechanics it is important not to make things more complicated than necessary. For our products we always used the rule: The simpler the better.
The stiffness of springs, strings and a stringbed is a static value. How much force is needed to create a certain deflection in kg/cm or lbs/inch.

Calculating the stiffness from an impact or vibration makes the measurement only more complicated and less accurate.

 

[jdawgg]

IMO: In mechanics it is important not to make things more complicated than necessary. For our products we always used the rule: The simpler the better.
The stiffness of springs, strings and a stringbed is a static value. How much force is needed to create a certain deflection in kg/cm or lbs/inch.

Calculating the stiffness from an impact or vibration makes the measurement only more complicated and less accurate.

Do you have a test method to determine coefficient of friction of string to string and string to ball?

I think if you’re consistent with your test method, your stiffness values will give you a general idea of how different strings compare, but might not match TW stiffness values if they tested differently.

 

[fritzhimself]

It's not exactly a DIY device - you have to measure it yourself:

Pro T One Mini String Lab – string test machine – STRINGLAB

stringlab.it

 

[ryohazuki222]

It's not exactly a DIY device - you have to measure it yourself:

Pro T One Mini String Lab – string test machine – STRINGLAB

stringlab.it

Any chance you speak Italian?

Can’t quite figure out how the machine works and what that small circular pad is in the middle that would lie under the string.

 

[BlueB]

Just an idea:
Pull a single string using a frame and stringing machine, to a refrence tension, pluck it and measure frequency using a guitar tuning app on the phone?

 

[ryohazuki222]

Sounds like you’re more interested in string elongation only. If you’re going to stretch a string under tension it will be hard to duplicate a sudden impact with the hammer / pendulum of some kind. You could use a DW and with the string under tension add or drop another weight.

Did some digging on my end to actually figure out a better way to describe what I’m trying to do after looking over what you sent and doubling back on some twu articles and experiments I haven’t looked at in a while.

Basically;
I want to measure the dynamic stiffness of a string at a given tension and simulated impact. If I understand correctly how twu is doing this; I want someway to hold a string at a given tension that I can control. I want someway to impact that string consistently. I want some way to measure how much stretch the string undergoes during impact under tension (ie; how long the string gets).

 

[travlerajm]

20 years ago, I borrowed a few dozen racquets from the local pro shop and did stiffness measurements on them in 2 directions.

I cantilevered the racquet over the edge of a rigid countertop, clamped the handle to the edge of the counter with a pair of C-clamps. Then suspended a 1/2 gallon jug of OJ from the center of the stringbed.

I measured the deflection in mm, both in the plane of the stringbed, and with tension pulled perpendicular to stringbed.

My a priori hypothesis was that TW Review scores for topspin would correlate with the ratio of x:y, where x was in-plane stiffness, and y was normal stiffness.

The results supported my hypothesis to a T.

 

[fritzhimself]

Any chance you speak Italian?

Can’t quite figure out how the machine works and what that small circular pad is in the middle that would lie under the string.

I don't speak Italian - but there are plenty of translation programs that can do it for you.

 

[Stringway Official]

This is the Google translation of the description:
The mini string lab pro-t-one is a handy, simple and innovative tool that opens the doors to all technicians, stringers, enthusiasts and players who want to directly test and carry out various types of experiments on the strings that they usually mount or that they would like to mount on their equipment. The tool, although apparently simple, is made with precautions that allow for experiments and precision tests using a body made of stainless steel sheet and precision mechanics as well as a dynamometer of proven reliability that allows the repeatability of the values and measurements performed, allowing a safe comparison with the field behavior of the strings, whatever material they are. The mini string lab comes with a sophisticated spreadsheet that allows for the creation of a complete report of the test performed on the string. manual here
This is the link to the manual:
http://www.pro-t-one.it/wp-content/uploads/2014/06/mini-string-lab.pdf

The pictures may show what it does.

You can also enter the Italian text into Google translate to obtain an English text.
It looks interesting

 

[Stringway Official]

This table shows what the tool does: It measures the stiffness in steps in kg/mm.